In recent years, as part of an approach to address environmental issues, a hybrid vehicle capable of running by a driving force received from a rotating electric machine is increasingly gaining attention. When such hybrid vehicle is to be accelerated, it utilizes a driving force received from the engine to gain acceleration, generate power supplied to the rotating electric machine, and the like. Accordingly it requires a rapidly increased number of rotations of the engine.
Japanese Patent Laying-open No. 10-238380 discloses a control device for a hybrid vehicle that allows improved responsiveness of its engine in a transient operation of the vehicle. More specifically, as described in Japanese Patent Laying-open No. 10-238380, the control device for a hybrid vehicle controls a hybrid vehicle including an engine, a power conversion unit coupled to the engine and including first and second rotating electric machines, an inverter device for driving the first and second rotating electric machines, and an electric storage device electrically connected to the inverter device. The control device controls a torque output from the engine, as based on information of how the vehicle is operated, and the control device also controls the value of a torque that the first and second rotating electric machines are controlled to generate, as based on the amount by which the torque that the engine outputs is controlled and a target number of rotations of the engine that corresponds to a characteristic of the engine. The control device includes a detection unit detecting a transient state, and a torque correction unit. The detection unit detecting a transient state detects those transient states of the vehicle which correspond to the vehicle's acceleration and deceleration. If a transient state detected as a result indicates that the vehicle is accelerated, the torque correction unit makes a correction to decrease the value of a torque that the first rotating electric machine is instructed to output, and also makes a correction to increase the value of a torque that the second rotating electric machine is instructed to output. If the transient state detected as a result indicates that the vehicle is decelerated, the torque correction unit makes a correction to increase the value of a torque that the first rotating electric machine is instructed to output, and also makes a correction to decrease the value of a torque that the second rotating electric machine is instructed to output.
As described in the publication, the control device for a hybrid vehicle is provided such that the engine rotates with the first rotating electric machine acting as a load. If in such a case the vehicle is accelerated, and the value of a torque that the first rotating electric machine is instructed to output is corrected to decrease, the load of the engine is alleviated by that decrease, and this facilitates increasing the number of rotations of the engine. At the time, the value of a torque that the second rotating electric machine is instructed to output is corrected to increase, and the vehicle's running performance will not be impaired. In contrast, if the vehicle is decelerated, and the value of a torque that the first rotating electric machine is instructed to output is corrected to increase, the load of the engine is increased by that increase, and this facilitates decreasing the number of rotations of the engine. At the time, the value of a torque that the second rotating electric machine is instructed to output is corrected to decrease, and the vehicle is braked appropriately. Thus if the engine is in the transient operation, poor emission, an output of the engine accidentally reduced, and other disadvantages can be resolved. As a result the engine can provide an output as required, and thus be improved in responsiveness.
If the engine and the first and second rotating electric machines are coupled in some manner, decreasing the first rotating electric machine in torque when the vehicle is accelerated, as done by the control device for a hybrid vehicle, as described in Japanese Patent Laying-open No. 10-238380, can increase the engine's load. For example, if the engine is coupled to a carrier of a planetary gear, and the first and second rotating electric machines are coupled to a sun gear and a ring gear, respectively, then, as indicated in the nomographic chart of FIG. 7 by a solid line, the first and second rotating electric machines have their respective numbers of rotations in a relationship bound by a straight line. If in such a case the first rotating electric machine decreases in torque and hence the number of rotations, then, as indicated in FIG. 7 by a chained line, the first rotating electric machine acts as a load and the engine has its number of rotations pulled down. As such, when the vehicle is accelerated, the engine cannot provide increased driving force, and as a result, acceleration as desired may not be obtained.